Abstract
The improvement of the operating flexibility of a thermal power unit has always been an essential issue due to its substantial support to power system stability. In addition, this issue has become increasingly important for the large-scale integration of fluctuant wind energy. The feedwater bypass (FWB) is an effective method for raising the load-following capability of a power unit by quickly activating its thermal storage system. However, understanding the dynamic characteristics of the FWB and designing appropriate control strategies for this method remain as challenges. In this paper, mathematical models that describe the static and dynamic characteristics of the FWB in unit power output are presented and discussed. Then, an optimized control strategy for improving a power unit's load-following capability is developed by combining FWB and the traditional coordinated control strategy (CCS). Last, field tests on a 300-MW power unit show that the unit ramp rate can be raised to twice that in traditional CCS using the improved strategy. Moreover, the strategy can be extensively used in coal-fired units for the flexible power regulation and the primary frequency control of power grids.
Highlights
Grid-connected units are required to provide a primary frequency reserve to electricity grids by adjusting their power production to respond to load demand changes [1], [2]
Flexible improvement is planned for a coal-fired generation of approximately 219 million kW by 2020
DYNAMIC MODEL As discussed above, two static stage models are provided to illustrate the influence of feedwater bypass (FWB) on power output
Summary
Grid-connected units are required to provide a primary frequency reserve to electricity grids by adjusting their power production to respond to load demand changes [1], [2]. Coal-fired units adopt the boiler–turbine coordinated control strategy (CCS) to regulate turbine power output by using thermal storage in the boiler system [7]. Given that a rapid electric power response is required to integrate large-scale renewable energy sources, additional stored energy must be activated, because an increase in electrical power output due to an increase in fuel input is extremely slow Various measures, such as turbine exhausted steam, extraction steam [21], condensation water, and feedwater flow controls [22], [23], can result in rapid power response. Lausterer [25] conducted dynamic simulations on an entire 660 MW supercritical coal-fired power plant using GSE software, and the feedwater bypass (FWB) method was analyzed and compared with the HP extraction steam throttling method.
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